Modelling Urban-Scale Population Exposure To Reactive Air Toxics, Does chemical transformation need to be considered?
Human health impacts resulting from exposure to ambient concentrations of air toxic compounds are coming under increasing levels of scrutiny. The Australian National Environment Protection Council has identified five priority air toxics- benzene, toluene, formaldehyde, xylene’s and PAH’s which are currently the subject of observation and modelling to determine hotspots in urban airsheds.
Of these compounds, formaldehyde, toluene and the xylenes are known to be strongly chemically reactive. However, urban-scale air toxic modelling undertaken in Australia has traditionally treated such air toxics as non-reactive. In the case of toluene and xylene, this may lead to systematic over estimates of population exposure. In the case of formaldehyde, which is both a primary and a secondary pollutant, it is less clear as to either the sign or the magnitude of the error.
In this paper, we present the outcomes of a project sponsored by the Australian Department of Environment and Heritage. The project makes use of recent advances in affordable, high-performance computational capacity to run 12-month, urban-scale simulations of reactive air toxics using a 3-dimensional model with a comprehensive chemical transformation mechanism. We report on the verification of the model performance for Melbourne, Victoria using ambient air toxic data sets, and then go on to consider the magnitude of the error which may result from using the ‘non-reactive’ approximation to model urban population exposures for the three reactive air toxic compounds.